The principal objective of the proposed research is to develop a fundamental understanding of the regulation of NO (nitric oxide) formation in vascular tissue. Now that vascular endothelial cells and many other cell types have been shown to release NO, attention is being focused on the biosynthesis, metabolism, and actions of NO in diverse cell types and tissues. It is clear that L-arginine serves as at least one precursor to endogenously formed NO. The focus of this proposal is on the biosynthesis of NO from L-arginine by vascular endothelial cells and vascular smooth muscle cells, and on important factors that influence this unique biochemical process, such as electrical field stimulation and L-arginine transport. Although it is well appreciated that NO acts on target cells to stimulate cyclic GMP production and thereby elicit a cellular response, this proposal will examine also the functional consequences of elevated cyclic GMP levels in cells of origin of NO. NO generated within its cells of origin elevate cyclic GMP levels and this could modulate cellular function. The central hypothesis is that NO can be synthesized by a unique enzyme system (NO synthase) present in vascular endothelial cells, vascular smooth muscle cells, and perhaps nonadrenergic-noncholinergic neurons in response to chemical agents, shear forces, and electrical stimulation, and that this process can be regulated by calcium, calmodulin, and L-arginine transport. FIVE Specific Aims are proposed to achieve the objective: (1) to characterize and purify NO synthase from vascular endothelial cells, (2) to characterize muscle-derived relaxing factor (MDRF) from vascular smooth muscle cells, (3) to elucidate the mechanism by which electrical field stimulation causes vascular smooth muscle relaxation, (4) to ascertain the biological actions of NO and S-nitroso-L-cysteine directly on their cells of origin, and (5) to elucidate the role of L-arginine transport in endothelium-dependent relaxation and NO generation. These objectives and aims represent a continuing long-term effort to understand the physiological and pathophysiological significance of endogenous NO in vascular and other tissues, which could lead in turn to a better understanding of the etiology and therapy of cardiovascular disorders including essential hypertension, vasospasm, and stroke.